Arcus is a proposed NASA Medium Explorer mission that aims
to significantly improve our spectroscopic capabilities using soft X-ray gratings.
With spectral resolution \(R>\) 2500 between 12-50 \(\mathring{A}\) , the
Arcus proposal possesses the ability to resolve the absorption of a
diverse range of metal species in the extended halos of galaxies,
groups, and clusters along sight lines toward distant quasars
[1]}. X-ray grating spectroscopy provides a critical
complementary probe to planned micro-calorimeters by having \(\sim 10\times \)  greater resolution and probing the diffuse hot gas
comprising the majority of missing metals and baryons
[2]}, [3]}. Arcus is designed to achieve a 10-fold
increase in sensitivity (i.e. square root of effective area times
resolution) over existing grating spectrometers on Chandra and XMM-Newton.
